This invention relates to a starter with a reduction gear which is employed for vehicles such as motor vehicles, and more particularly to an overhang type starter with its pinion protruded in front of the front bracket.
An overhang type starter with a reduction gear is known in the art in which its pinion is moved forwardly through the front bracket to engage with the ring gear of an engine thereby to start the engine.
FIG. 7 is a longitudinal section of a conventional starter of this type. In FIG. 7, reference numeral 1 designates a DC motor which is designed as follows: The DC motor 1 has a housing 2, on which a field system 3 comprising permanent magnets or field coils is mounted. An armature core 4 having an armature coil assembly 5 is securely fixed on an armature shaft 6. A small gear, namely, a sun gear 6a is formed on one end portion of the armature shaft 6. The DC motor further comprises: a commutator 7; brush units 8, and a rear bracket 9 coupled to the housing 2, thus supporting the rear end portion of the armature shaft 6 through a bearing 10.
A front bracket 12 is coupled to the housing 2. A planetary speed reduction gear unit 14 is arranged coaxially with the DC motor 1. The planetary speed reduction gear unit 14 is designed as follows: An internal gear frame 15 having an internal gear 15a is fixedly secured to the front bracket 12. A plurality of plant gears 16 are engaged with the sun gear 6a and the internal gear 15a in such a manner that it revolves around the sun gear while rotating themselves to reduce the speed of rotation. The planet gears 16 are mounted through bearings 18 on supporting pins 17 which are embedded in a carrier 19a like a flange which is formed on the output shaft 19 of the starter.
The front end portion of the armature shaft 6 is supported through a bearing 20 by the wall of a hole formed in the end face of the output shaft 19, with a steel ball 21 held in the hole in such a manner that the front end portion is engaged through the steel ball with the armature shaft 6. The rear end portion of the output shaft 19 is supported through a bearing 22 by the internal gear frame 15.
Further in FIG. 7, reference numeral 24 designates an overrunning clutch. The clutch 24 comprises: a clutch outer 25, which is engaged with a helical spline gear 19b formed on the output shaft 19; and a clutch inner 26 coupled through rollers 27 to the clutch outer 25. The front end portion of the clutch inner 26 is formed into a pinion 28. An annular member 29 is secured to the clutch outer 25.
The clutch inner 26 is supported through a bearing 30 by the front bracket 12, and supports the front end portion 19 through a bearing 31. A stopper 32 is secured to the output shaft 19 at the end, so as to stop the forward movement of the over-running clutch 24. More specifically, the over-running clutch 24 is moved in the forward direction until the step 26a of the clutch inner 26 abuts against the stopper 32.
An electromagnetic switch 34 is mounted on the housing 2, which is designed as follows: That is, the electromagnetic switch 34 comprises: an exciting coil 35 wound on a bobbin; a stationary iron core 36; a movable iron core, namely, a plunger 37 confronted with the stationary iron core 36; a movable supporting rod 38 supported by the stationary iron core 36 in such a manner that it penetrates the latter, the rod 38 supporting a movable contact 39 through an insulator; a pair of stationary contacts 40 mounted on a cap 41 made of an insulating material in such a manner that they confront with the movable contact 39; and a return spring 42 interposed between the stationary iron core 36 and the plunger 37, to return the plunger to the forward position. The electromagnetic switch 34 further comprises: a hook 43 held inside the plunger 37 in such a manner that its end locking portion 43a is protruded outside; a shift lever 44 in the form of a fork which is supported with its middle portion as a fulcrum portion, the shift lever 44 having one end portion which is engaged with the end locking portion 43a and the other end portion, namely, two prongs which are engaged with the aforementioned annular member 29 secured to the clutch outer 25; and a compression spring 45 provided inside the plunger 37 to urge the hook 43 backwardly.
In the conventional starter thus constructed, upon energization of the exciting coil 35, the plunger 37 is moved towards the stationary iron core 36, so that the shift lever 44 is turned counterclockwise with the aid of the hook 43; that is, the over-running clutch is moved in the forward direction. As a result, the pinion 28 is engaged with the ring gear of the engine. At the same time, the DC motor 1 is started, and the rotation of the armature shaft 6 is transmitted through the planetary speed reduction gear unit 14 to the output shaft 19. The rotation of the output shaft 19 is transmitted through the over-running clutch 24 to the pinion 28, thus starting the engine.
The conventional starter is disadvantageous in the following points:
The over-running clutch 24 moved by the shift lever 44 has the pinion 28 which is relatively large in weight. Therefore, if the elastic force of the compression spring 45 is not large enough to push the pinion 28 towards the ring gear of the engine, then the pinion 28 is not correctly engaged with the ring gear, with the result that the end face of the ring gear is scraped.
This difficulty may be eliminated by increasing the elastic force of the compression spring 45 in correspondence to the weight of the over-running clutch 24 including the pinion 28. In this case, it is necessary to increase the electromagnetic force of the electromagnetic switch 34 in correspondence to the elastic force thus increased. The increase of the electromagnetic force results in an increase in volume of the electromagnetic switch. Thus, the resultant starter is limited in the installation on an engine.
The clutch inner 26 is formed at its front end portion with the pinion 28 and an axial hole 28b the diameter of which is set so that the stopper 32 is fitted inside of the axial hole 28b. Accordingly, the size of the teeth or the number of the teeth of the pinion 28 is restricted in view of the fact that the thickness below the dedendum circle of the teeth is secured. Hence, in order to increase the size of teeth or to decrease the number of teeth of the pinion 28, it is necessary to increase the outside diameter of the front end portion of the pinion 28. In this case, unavoidably the over-running clutch is increased in weight, and the electromagnetic switch is increased in volume. Therefore, the size of teeth or the number of teeth of the pinion 28 is generally determined from the structure of the starter, and accordingly the gear ratio of the ring gear to the pinion 28 is limited, which greatly limits the degree of freedom in designing starting characteristics for an engine.